Water activity detection device and method based on waterproof breathable film

Abstract

The invention belongs to the technical field of water activity detection, and particularly relates to a water activity detection device and method based on a waterproof breathable film, and the device comprises a containing shell which is used for containing a sample to be detected; the vent hole is formed in the bottom of the accommodating shell and used for volatilizing water vapor from the sample; when a sample is detected, the waterproof breathable film is used for permeating water vapor and preventing liquid or particles of the sample from leaking, the temperature and humidity sensor is used for obtaining first data and second data, and a baffle used for separating the air hole from the sample is installed in the middle of the bottom wall of the containing shell. A water vapor runner is reserved between the top of the baffle and the top of the accommodating shell; the method comprises the steps of 1 to 4, installing equipment, checking the integrity of the equipment, and electrifying and preheating the equipment. The device adopting the embedded membrane and having a simple structure is low in maintenance cost, can quickly capture water vapor released by the sample and is beneficial to improving the measurement accuracy by combining temperature compensation.

Description

Technical Field

[0001] The present invention belongs to the technical field of water activity detection, and in particular relates to a water activity detection device and method based on a waterproof breathable membrane. Background Art

[0002] Water activity (Aw) refers to the ratio of the water vapor partial pressure at the surface of a material (such as food) to the saturated vapor partial pressure of pure water at the same temperature. Its value usually ranges between 0 and 1, reflecting the degree to which the water in the material is available to microorganisms, enzymes, etc. It has a key impact on food preservation, microbial growth, chemical reaction rate and final product quality.

[0003] Taking the water activity test of food as an example, a food sample is placed in a container. The humidity signal is directly measured by the humidity sensor inside the container. The humidity at different time points is compared to analyze the water activity of the food, as shown in the following example: A search revealed a Chinese invention, publication number CN120064363A, that describes a water activity testing device and method for Cantonese-style mooncakes. This device places a testing box on the mooncake transport line and uses internal fan-shaped plates to perform capacitive water activity testing on the front and back of the mooncakes, as well as an electromagnetic wave sensor to perform microwave water activity testing on the sides. This combination enables comprehensive water activity testing of the mooncakes. However, each batch of mooncakes uses the same ingredients and has relatively similar water activity. Testing each batch individually would not only waste testing resources but also slow down the mooncake transport cycle. A search revealed a Chinese invention with publication number CN114778377A, which describes an efficient water activity tester and method for snowy mooncakes. Multiple mooncakes can be placed in the device at one time, and the sensors are used to detect the mooncakes one by one by moving them up and down. After the test, the space containing the mooncakes is evacuated to reduce residue. However, powder may accumulate on the surface of mooncakes and other foods, which can float onto the sensor and gather there, obstructing water vapor and reducing the accuracy of water activity detection.

[0004] In summary, the present invention proposes a water activity detection device and method based on a waterproof and breathable membrane, which has a simple overall structure, low maintenance cost and high measurement accuracy. Summary of the Invention

[0005] The purpose of the present invention is to provide a water activity detection device and method based on a waterproof and breathable membrane. The device adopts a simple structure of an embedded membrane, has low maintenance cost, can quickly capture the water vapor released by the sample and combines temperature compensation, which is conducive to improving measurement accuracy.

[0006] The technical solutions adopted by the present invention are as follows: A water activity detection device based on a waterproof and breathable membrane, comprising: A containing shell, used for containing the sample to be tested; The vent hole at the bottom of the housing is used for evaporating water vapor from the sample; The waterproof and breathable membrane and the temperature and humidity sensor are arranged in the vent hole. When the sample is tested, the waterproof and breathable membrane is used to pass water vapor and prevent the liquid or particles of the sample from leaking. The temperature and humidity sensor is used to obtain the first data and the second data.

[0007] As an optional solution, a baffle for separating the air vent and the sample is installed in the middle of the bottom wall of the accommodating shell, and a water vapor flow channel is left between the top of the baffle and the top of the accommodating shell.

[0008] A method for detecting water activity based on a waterproof breathable membrane comprises the following steps: Install equipment, check equipment integrity, power on and preheat equipment; Selecting a calibration medium to calibrate the device, obtaining first data, adopting a temperature compensation strategy based on the first data during calibration, and improving the accuracy and stability of the calibration result through retesting; Place the sample in the device, perform the test, obtain the second data, correct the first data based on the second data, and calculate the water activity value; Repeat the measurement and compare different measurement results to verify accuracy.

[0009] As an optional solution, in the step of installing the device, the waterproof breathable membrane is evenly covered on the vent hole at the bottom of the housing, and the edge of the waterproof breathable membrane is fixed with a sealing ring to ensure that the waterproof breathable membrane is seamlessly fitted around the vent hole without wrinkles; At the same time, the temperature and humidity sensor is installed in the air vent at a certain distance below the waterproof breathable membrane. The outer side of the temperature and humidity sensor is fixed by a built-in bracket or sealing ring to prevent the temperature and humidity sensor from contacting the surface of the waterproof breathable membrane.

[0010] As an optional solution, during the process of checking the integrity of the equipment, first, visually check whether the outer surface of the housing is intact and whether there are gaps in the waterproof and breathable membrane; Secondly, turn over the container shell for inspection, with the vent hole facing upwards, and pour an appropriate amount of clean water onto the waterproof breathable membrane. After a certain period of time, observe whether the water level drops. If the water level does not drop significantly, the equipment is intact; if the water level drops, it indicates that the container shell is leaking and there are gaps in the equipment, and the sealing ring or waterproof breathable membrane needs to be replaced.

[0011] As an optional solution, the calibration medium is any one of a saturated lithium chloride solution, a saturated magnesium chloride solution, a saturated cobalt chloride solution or a saturated potassium chloride solution.

[0012] As an optional solution, during the calibration process, an appropriate amount of standard salt solution is placed inside the container to ensure that the surface area of ​​the solution is in contact with the air below the waterproof breathable membrane, so that a closed environment is formed below the waterproof breathable membrane and above the solution. Then, the housing is sequentially placed in temperature environments with different gradients, and the temperature is allowed to stabilize, and the temperature and humidity sensor readings are recorded as first data; In the calibration module or software interface of the device, calculate the difference between the water activity value actually measured by the temperature and humidity sensor and the known water activity value of the standard salt solution.

[0013] As an optional solution, the temperature compensation strategy is based on the difference between the water activity value actually measured by the temperature and humidity sensor and the known water activity value of the standard salt solution. The same operation is performed at the required temperature points in turn to complete the compensation parameter fitting for the entire temperature range. The fitting value is recorded as .

[0014] As an optional solution, during the test, select Start Measurement in the device control interface or software. The temperature and humidity sensor will automatically collect the humidity and temperature values ​​of the small space below the waterproof breathable membrane. The temperature value is used as the second data. According to the set sampling frequency, the device continuously records the humidity and temperature data. At the same time, the relative humidity of the sample environment is measured in real time by the temperature and humidity sensor, recorded as RH, and converted into water activity .

[0015] As an optional solution, in the process of combining the second data to correct the first data, after real-time data acquisition, the data processing module will call the temperature compensation function to correct the humidity reading and convert it into water activity value. .

[0016] The technical effects achieved by the present invention are: By adding a waterproof and breathable membrane at the bottom of the accommodating cavity and arranging a temperature and humidity sensor underneath it, the present invention can quickly capture water vapor released by the sample, effectively shorten the equilibrium time, and introduce a temperature compensation function to ensure the consistency of measurement data at different room temperatures, thereby significantly improving measurement accuracy and reliability. In addition, compared with high-end equipment such as the chilled mirror dew point method, the equipment structure adopted by the present invention is simpler, the equipment cost is lower, and it is not easily affected by mirror contamination. It is only necessary to check the integrity of the waterproof and breathable membrane and the performance of the temperature and humidity sensor on a daily basis, and regularly calibrate the temperature compensation function with a standard salt solution to maintain stable operation, thereby reducing maintenance costs.

[0017] The present invention can meet the requirements of air permeability and stain resistance for different samples, such as solids, powders, semi-solids, etc. by selecting waterproof and breathable membranes with different pore sizes or thicknesses. The temperature compensation function enables the equipment to maintain high-precision measurement under various ambient temperatures, making it more adaptable. Functional modules such as constant temperature, automatic cleaning or multi-parameter monitoring can also be added, making it suitable for different industrial and laboratory application scenarios.

[0018] The present invention uses standard salt solutions for calibration at different room temperatures to ensure that the device can provide consistent and accurate water activity measurement results under various temperature conditions. The temperature compensation function automatically adjusts the measurement data to eliminate errors caused by temperature fluctuations, improving the consistency and reliability of the overall measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 1 is a longitudinal cross-sectional view of a water activity detection device based on a waterproof breathable membrane in Example 1 of the present invention; Figure 2 is a longitudinal cross-sectional view of the air vent in the first embodiment of the present invention; Figure 3 is a system block diagram of the temperature and humidity sensor in embodiment 1 of the present invention; Figure 4 This is a flow chart of a water activity detection method based on a waterproof breathable membrane in embodiment 2 of the present invention.

[0020] In the accompanying drawings, the components represented by the reference numerals are as follows: 1. Container; 2. Baffle; 3. Ventilation hole; 4. Waterproof and breathable membrane; 5. Temperature and humidity sensor. DETAILED DESCRIPTION

[0021] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is described in detail below with reference to the following examples. It should be understood that the following text is only used to describe one or more specific embodiments of the present invention and does not strictly limit the scope of protection of the present invention.

[0022] This application takes a mooncake food factory as an example. When it has two automated production lines, it can produce about 100,000 mooncakes a day. The traditional handmade mooncake production line can produce 40,000 mooncakes a day. In the mooncake processing process, the materials used in each batch of mooncakes are extremely similar. For example, the filling is generally made by mixing and stirring in a tank of mixed materials, and the moisture, sweetness or saltiness of each part is not much different. The mooncake skin is generally squeezed out of the same dough, and the hardness, moisture, sweetness, etc. are not much different. Therefore, the mooncakes coming off the production line are often inspected by random sampling, which is more time-saving and labor-saving, and does not require a full inspection.

[0023] Example 1: like Figure 1-Figure 3As shown, a water activity detection device based on a waterproof breathable membrane includes a containing shell 1. The containing shell 1 based on an inert material can be opened from the bottom to accommodate a sample to be tested; an air vent 3 is provided at the bottom of the containing shell 1 for the sample to volatilize water vapor; a waterproof breathable membrane 4 and a temperature and humidity sensor 5 are arranged at the air vent 3. When testing the sample, an appropriate amount of sample is taken and placed in the inner cavity of the containing shell 1 and piled to a certain height, and then the containing shell 1 is covered. The moisture on the surface and inside of the sample will form a local relative humidity in the containing cavity through the diffusion and evaporation process, and escape outward along the air vent 3. Since the waterproof breathable membrane 4 is used to pass water vapor and block the leakage of liquid or particles in the sample, water vapor can pass through the waterproof breathable membrane 4 without letting the sample itself or other liquid components leak. At this time, the HIH-4000 model temperature and humidity sensor 5 can be used to obtain the humidity signal to calculate the water activity.

[0024] Among them, the inert material can be glass, stainless steel or plastic, the containing shell 1 can be made into a cup shape, the bottom of the cup is in the shape of a cup lid that can be opened along a thread, and the inner wall of the cup is smooth and easy to clean to avoid contamination of the sample; the waterproof and breathable membrane 4 can be selected from PTFE (polytetrafluoroethylene) membrane, PES (Polyethersulfone, polyethersulfone) membrane, silicone membrane, nylon membrane, PP (Polypropylene, polypropylene) membrane, cellulose-based membrane and ePTFE ethylene (expanded polytetrafluoroethylene) membrane.

[0025] Furthermore, the temperature and humidity sensor 5 synchronously measures the temperature signal of the environment in which the accommodating shell 1 is located, thereby ensuring the accuracy of the water activity calculation.

[0026] Refer to the attached Figure 2 and Figure 3 For some fluid samples with fluidity, this embodiment installs a baffle 2 in the middle of the bottom wall of the accommodating shell 1 to separate the air vent 3 and the sample. The fluid sample is placed on one side of the baffle 2, and the air vent 3 is left on the other side of the baffle 2. Then the accommodating shell 1 is closed. Since a water vapor flow channel is left between the top of the baffle 2 and the top of the accommodating shell 1, the water vapor volatilized by the fluid sample can pass through the air vent 3 while ensuring that the fluid sample does not overflow, providing a stable environment for the detection of the fluid sample.

[0027] Refer to the attached Figure 3 , this embodiment also includes: The calibration module is used to place the container 1 before the sample is tested and calibrate with a standard salt solution at a temperature of 25°C. The standard salt solution is, for example, a saturated lithium chloride solution with a water activity of 0.113, a saturated magnesium chloride solution with a water activity of 0.328, a saturated cobalt chloride solution with a water activity of 0.649, or a saturated potassium chloride solution with a water activity of 0.843 at 25°C, to ensure the measurement accuracy of the device at a temperature of 25°C; The temperature compensation processing module is used for temperature compensation during sample testing. It uses the same standard salt solution to measure water activity at different temperatures, calculates the difference between the measured data and the data at 25°C, fits the temperature compensation function, and performs temperature compensation processing on the data collected by the humidity sensor to ensure the consistency of the measured data at different room temperatures. The control and display module includes a data acquisition circuit, a data processing unit, and a display terminal. The data processing unit is built into the motherboard of the real terminal and is connected to the temperature and humidity sensor 5 using a data acquisition circuit. It is used to process and convert the humidity and temperature signals, such as an AD converter, and output the water activity value. If needed, it can also be equipped with a storage module and a communication module, such as a USB interface or a Bluetooth module, to facilitate data recording and remote monitoring. The power supply part can be powered by a DC power supply or a battery to power the temperature and humidity sensor 5, the temperature compensation processing module, the control and display module, the storage module and the communication module to meet the needs of rapid on-site detection or fixed laboratory scenarios.

[0028] Example 2: The following methods are commonly used to measure water activity in the food industry: 1. Equilibrium relative humidity method: The sample is placed in an environment with known relative humidity. After the system reaches moisture equilibrium, the water activity of the sample is calculated based on the ambient humidity. The advantage of this method is that it is simple and easy to operate, but the disadvantages are obvious. The measurement time is long, the measurement results are greatly affected by the environment, and the accuracy is not high. 2. The chilled mirror dew point method uses a chilled mirror sensor to detect the dew point temperature of the sample's surrounding environment, and calculates the relative humidity based on the dew point temperature to obtain the water activity. It has the advantages of high precision and fast response speed, but the disadvantages are high equipment cost and high manual operation requirements.

[0029] Therefore, in order to conveniently detect the water activity of the sample, based on the water activity detection device in Example 1, the following detection method is adopted, which can introduce a temperature compensation function to ensure the consistency of the measurement data at different room temperatures, thereby quickly and accurately obtaining the sample water activity value.

[0030] like Figure 4 As shown, a water activity detection method based on a waterproof breathable membrane includes the following steps: S1. Prepare for installation: S101. Install the waterproof breathable membrane 4: Flatly cover the breathable hole 3 at the bottom of the housing 1 with the waterproof breathable membrane 4 and secure the edge of the waterproof breathable membrane 4 with a sealing ring or other clamping structure to ensure that the waterproof breathable membrane 4 fits seamlessly around the breathable hole 3 without wrinkles or looseness. S102. Install the temperature and humidity sensor 5: Install the temperature and humidity sensor 5 in the vent hole 3 at a certain distance below the waterproof breathable membrane 4. The outer side of the temperature and humidity sensor 5 can be fixed with a built-in bracket or sealing ring to prevent the temperature and humidity sensor 5 from contacting the surface of the waterproof breathable membrane 4. S103. Check the integrity of the equipment: First, visually inspect the housing 1 to see if it is intact and whether there are any gaps in the waterproof breathable membrane 4. If the housing 1 is incomplete, it needs to be scrapped, or if there are gaps in the waterproof breathable membrane 4, it needs to be reinstalled. If the housing 1 is intact and the waterproof breathable membrane 4 has no gaps, then the equipment is in good condition and the experiment can continue. Next, turn over the housing 1 for inspection, with the vent 3 facing upward, and pour a proper amount of clean water onto the waterproof breathable membrane 4. After a certain period of time, observe whether the water level drops. If the water level does not drop significantly, the equipment is intact. If the water level drops, it indicates that the housing 1 has leaked and there is a gap in the equipment, and the sealing ring or waterproof breathable membrane 4 needs to be replaced. S104, power on and preheat the device: connect the power supply, turn on the device power switch, and put the data processing module, temperature and humidity sensor 5 and display terminal into working state; Generally, the temperature and humidity sensor 5 has a short warm-up time, which may take several minutes. During this period, formal measurements should be avoided. Measurements can only be started after the output of the temperature and humidity sensor 5 is stable. S2. Calibration and temperature compensation equipment: S201. Select the calibration medium: Based on the test range and required accuracy, select a standard salt solution, such as a saturated lithium chloride solution with a water activity of 0.113 at 25°C, a saturated magnesium chloride solution with a water activity of 0.328, a saturated cobalt chloride solution with a water activity of 0.649, or a saturated potassium chloride solution with a water activity of 0.843. Among them, prepare a temperature-controlled environment, and place the installed housing 1 stably in a test environment, such as a GDW-100 constant temperature box, to perform calibration at a constant temperature and humidity; S202. Place standard salt solution: Place an appropriate amount of standard salt solution inside the container 1. The amount of standard salt solution is determined by the size of the container and the position of the temperature and humidity sensor 5. Ensure that there is enough surface area of ​​the solution to contact the air below the waterproof breathable membrane 4, so that a closed environment is formed below the waterproof breathable membrane 4 and above the solution. S203, multi-temperature point calibration: placing the housing 1 in temperature environments of different gradients in sequence, waiting for the temperature to stabilize, and recording the readings of the temperature and humidity sensor 5 as first data; In the calibration module or software interface of the device, the difference between the water activity value actually measured by the temperature and humidity sensor 5 and the known water activity value of the standard salt solution is calculated; Perform the same operation at the required temperature points in turn to complete the compensation parameter fitting for the full temperature range. The calculation is as follows: in, is the relative humidity measured by the temperature and humidity sensor 5, is the current temperature, in °C, and All are nonlinear correction coefficients, determined through calibration experiments; Calibration using standard salt solutions at different room temperatures ensures that the device can provide consistent and accurate water activity measurement results under various temperature conditions. The temperature compensation function automatically adjusts the measurement data to eliminate errors caused by temperature fluctuations, improving the consistency and reliability of the overall measurement. S204, calibration result confirmation: After completing calibration at all target temperatures, one or more temperature points can be selected and retested with the same standard salt solution to verify the accuracy and stability of the calibration results; S3. Sample testing: S301. Sample preparation: Homogenization: For powder, granular, paste or semi-solid samples, they can be ground, sieved or fully mixed as appropriate to obtain a representative sample; Temperature adjustment: If the sample needs to be tested at a specific temperature, it can be placed in a constant temperature condition or room temperature for a period of time in advance to avoid large temperature fluctuations after the test begins; S302, sample placement: Place an appropriate amount of prepared sample into the housing 1 so that it covers the bottom of the housing 1 and forms a closed space with the waterproof breathable membrane 4. This step can be done by hand, or a program can be used to schedule a five-axis / six-axis robot to take and place the sample and close the housing 1; S303. Start the test program: Select "Start Measurement" in the device control interface or software. The temperature and humidity sensor 5 will automatically collect the humidity and temperature values ​​of the small space below the waterproof breathable membrane 4. The temperature value is used as the second data. According to the set sampling frequency, such as once per second, the device continuously records the humidity and temperature data. At the same time, the relative humidity of the sample environment is measured in real time by the temperature and humidity sensor 5, and the relative humidity value is recorded as RH, which is converted into water activity according to the following formula. The water activity value is recorded as , calculated as follows: in, is the temperature of the sample, in °C, 、 、 、 、 and are constants obtained from calibration experiments, describing the nonlinear relationship between relative humidity and water activity and the effect of temperature; Corrected water activity calculation: After real-time data collection, the data processing module will call the temperature compensation function to correct the humidity reading and convert it into water activity. The corrected water activity value is recorded as , calculated as follows: In this way, the water activity value obtained is closer to the true value; S304, balance process monitoring: Different samples reach adsorption equilibrium or local saturation equilibrium at different speeds. The following judgment conditions can be set through the software: The humidity reading changes within a very small range, such as ±0.1%, in several consecutive samplings. ( is the relative humidity value recorded by the temperature and humidity sensor 5), indicating that adsorption equilibrium has been reached; Or according to the preset time, such as within 3 minutes to 5 minutes, if the monitoring change rate tends to zero, it means that the adsorption equilibrium has been reached. On the contrary, if the change rate does not tend to zero, it means that the adsorption equilibrium has not been reached; When the reading reaches the adsorption equilibrium state, the device can automatically determine that the measurement is completed and the final water activity value Lock or alert the operator; S305. Read and store results: When the device determines that the measurement is complete, the display terminal or software interface will pop up the current temperature, humidity, and water activity values. The user can choose to save the results immediately to the storage module or upload them to a computer or cloud via USB or wireless for archiving and further analysis. If multiple batches of samples need to be measured, the container can be emptied and the samples can be replaced to repeat the above steps. Alternatively, multiple tests can be performed in batch measurement mode in the software. S4. Data Analysis and Results: S401, Repeated measurement: To improve data reliability, it is recommended to measure the same sample at least 2 to 3 times. If the difference between the results is small, such as the measurement difference ≤ 0.005 ( is the water activity value before correction), the average value can be taken as the final measurement result; S402. Comparison with reference values: In R&D or quality control situations, the measurement results can be compared with the traditional equilibrium relative humidity method, the chilled mirror dew point method or known literature data to verify the accuracy of the device of the present invention.

[0031] In summary, the present invention adds a waterproof and breathable membrane 4 at the bottom of the accommodating cavity and arranges a temperature and humidity sensor 5 thereunder, which can quickly capture water vapor released by the sample, effectively shorten the equilibrium time, and introduce a temperature compensation function to ensure the consistency of measurement data at different room temperatures, thereby significantly improving measurement accuracy and reliability. In addition, compared with high-end equipment such as the chilled mirror dew point method, the equipment structure adopted by the present invention is simpler, the equipment cost is lower, and it is not easily affected by mirror contamination. It is only necessary to check the integrity of the waterproof and breathable membrane 4 and the performance of the temperature and humidity sensor 5 on a daily basis, and regularly calibrate the temperature compensation function with a standard salt solution to maintain stable operation, thereby reducing maintenance costs.

[0032] For different samples, such as solids, powders, and semi-solids, the requirements for air permeability and stain resistance can be met by selecting waterproof and breathable membranes 4 with different pore sizes or thicknesses. The temperature compensation function enables the device to maintain high-precision measurements under various ambient temperatures, making it more adaptable. Functional modules such as constant temperature, automatic cleaning, or multi-parameter monitoring can also be added to suit different industrial and laboratory application scenarios.

[0033] Moreover, the equipment used in the present invention can cooperate with the microprocessor and data acquisition module to realize automatic measurement, data recording, result calculation and alarm prompt. The introduction of temperature compensation function makes data processing more intelligent, reduces human intervention and improves the accuracy of data processing.

[0034] The foregoing merely represents optional embodiments of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained herein shall, unless otherwise specified or limited, be implemented in accordance with conventional means in the art.

Claims

1. A water activity detection device based on a waterproof breathable membrane, characterized in that: include: A housing (1) for accommodating a sample to be tested; A vent hole (3) is provided at the bottom of the housing (1) for evaporating water vapor from the sample; A waterproof breathable membrane (4) and a temperature and humidity sensor (5) are provided on the breathable hole (3); during sample detection, the waterproof breathable membrane (4) is used to allow water vapor to pass through and prevent liquid or particles of the sample from leaking; and the temperature and humidity sensor (5) is used to obtain first data and second data.

2. The water activity detection device based on a waterproof breathable membrane according to claim 1, characterized in that: A baffle (2) for separating the air vent (3) and the sample is installed in the middle of the bottom wall of the accommodating shell (1), and a water vapor flow channel is left between the top of the baffle (2) and the top of the accommodating shell (1).

3. A method for detecting water activity based on a waterproof breathable membrane, applied to a device for detecting water activity based on a waterproof breathable membrane according to any one of claims 1-2, characterized in that: The following steps are involved: Install equipment, check equipment integrity, power on and preheat equipment; Selecting a calibration medium to calibrate the device, obtaining first data, adopting a temperature compensation strategy based on the first data during calibration, and improving the accuracy and stability of the calibration result through retesting; Place the sample in the device, perform the test, obtain the second data, correct the first data based on the second data, and calculate the water activity value; Repeat the measurement and compare different measurement results to verify accuracy.

4. The method for detecting water activity based on a waterproof breathable membrane according to claim 3, wherein: In the step of installing the device, the waterproof breathable membrane (4) is evenly covered on the vent hole (3) at the bottom of the housing (1), and a sealing ring is used to fix the edge of the waterproof breathable membrane (4) to ensure that the waterproof breathable membrane (4) and the periphery of the vent hole (3) are seamlessly fitted and wrinkle-free; At the same time, the temperature and humidity sensor (5) is installed in the vent hole (3) at a certain distance below the waterproof breathable membrane (4), and the outer side of the temperature and humidity sensor (5) is fixed by a built-in bracket or a sealing ring to prevent the temperature and humidity sensor (5) from contacting the surface of the waterproof breathable membrane (4).

5. The method for detecting water activity based on a waterproof breathable membrane according to claim 3, characterized in that: During the process of checking the integrity of the equipment, first, visually check whether the outer surface of the housing (1) is intact and whether there are gaps in the waterproof and breathable membrane (4); Secondly, turn over the container (1) for inspection, turn the air vent (3) upward, and pour a proper amount of clean water into the waterproof breathable membrane (4). After a certain period of time, observe whether the water level drops. If the water level does not drop significantly, the equipment is intact. If the water level drops, it indicates that the container (1) has water seepage and there are gaps in the equipment, and the sealing ring or the waterproof breathable membrane (4) needs to be replaced.

6. The method for detecting water activity based on a waterproof breathable membrane according to claim 3, wherein: The calibration medium is any one of a saturated lithium chloride solution, a saturated magnesium chloride solution, a saturated cobalt chloride solution or a saturated potassium chloride solution.

7. The method for detecting water activity based on a waterproof breathable membrane according to claim 3, characterized in that: During the calibration process of the device, an appropriate amount of standard salt solution is placed inside the housing (1), ensuring that the surface of the solution has sufficient area to contact the air below the waterproof breathable membrane (4), so that a closed environment is formed below the waterproof breathable membrane (4) and above the solution; Then, the housing (1) is sequentially placed in temperature environments with different gradients, and the temperature is allowed to stabilize, and the readings of the temperature and humidity sensor (5) are recorded as first data; In the calibration module or software interface of the device, the difference between the water activity value actually measured by the temperature and humidity sensor (5) and the known water activity value of the standard salt solution is calculated.

8. The method for detecting water activity based on a waterproof breathable membrane according to claim 7, characterized in that: The temperature compensation strategy is based on the difference between the water activity value actually measured by the temperature and humidity sensor (5) and the known water activity value of the standard salt solution. The same operation is performed at the required temperature points in turn to complete the compensation parameter fitting of the entire temperature range. The fitting value is recorded as .

9. The method for detecting water activity based on a waterproof breathable membrane according to claim 8, characterized in that: During the test, the device controls the interface or software to start measuring, and the temperature and humidity sensor (5) automatically collects the humidity and temperature values ​​of the small space below the waterproof breathable membrane (4). The temperature value is used as the second data, and the device continuously records the humidity and temperature data according to the set sampling frequency. At the same time, the relative humidity of the sample environment is measured in real time by the temperature and humidity sensor (5), recorded as RH, and converted into water activity .

10. The method for detecting water activity based on a waterproof breathable membrane according to claim 9, characterized in that: In the process of combining the second data to correct the first data, after real-time data collection, the data processing module will call the temperature compensation function to correct the humidity reading and convert it into water activity value. .

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